In Situ Detecting Thermal Stability of Solid Electrolyte Interphase (SEI)

Solid electrolyte interphase (SEI) plays an important role in regulating the interfacial ion transfer and safety of Lithium‐ion batteries (LIBs). It is unstable and readily decomposed releasing much heat and gases and thus triggering thermal runaway. Herein, in situ heating X‐ray photoelectron spectroscopy is applied to uncover the inherent thermal decomposition process of the SEI. The evolution of the composition, nanostructure, and the released gases are further probed by cryogenic transmission electron microscopy, and gas chromatography. The results show that the organic components of SEI are readily decomposed even at room temperature, releasing some flammable gases (e.g., H 2 , CO, C 2 H 4 , etc.). The residual SEI after heat treatment is rich in inorganic components (e.g., Li 2 O, LiF, and Li 2 CO 3 ), provides a nanostructure model for a beneficial SEI with enhanced stability. This work deepens the understanding of SEI intrinsic thermal stability, reveals its underlying relationship with the thermal runaway of LIBs, and enlightens to enhance the safety of LIBs by achieving inorganics‐rich SEI.